1. Field of the Invention
The present invention relates to swallowable capsule cameras for imaging of the gastro-intestinal (GI) tract. In particular, the present invention relates to the control of the light sources in the camera.
2. Discussion of the Related Art
Devices for imaging body cavities or passages in vivo are known in the art and include endoscopes and autonomous encapsulated cameras. Endoscopes are flexible or rigid tubes that are passed into the body through an orifice or surgical opening, typically into the esophagus via the mouth or into the colon via the rectum. An image is taken at the distal end using a lens and transmitted optically to the proximal end located outside the body, either by a lens-relay system or by a coherent fiber-optic bundle. Alternatively, an instrument may record an image electronically at the distal end (e.g., using a CCD or CMOS array) and transfers the image data electrically to the proximal end through a cable. Endoscopes allow a physician control over the field of view and are well-accepted diagnostic tools. However, they have a number of limitations, present risks to the patient, and are invasive and uncomfortable for the patient. The cost of these procedures restricts their application as routine health-screening tools.
Because of the difficulty traversing a convoluted passage, endoscopes cannot reach the majority of the small intestine and special techniques and precautions—that increase cost—are required to reach the entirety of the colon. Endoscopic risks include the possible perforation of the bodily organs traversed and complications arising from anesthesia. Moreover, a trade-off must be made between patient pain during the procedure and the health risks and post-procedural down-time associated with anesthesia. Therefore, endoscopy is necessarily an in-patient service that involves a significant amount of time from clinicians and thus is a costly procedure.
An alternative in vivo image sensing technique is capsule endoscopy. In capsule endoscopy, a camera is housed in a swallowable capsule, along with a radio transmitter for transmitting data (which consists primarily of images recorded by the camera) to a base-station receiver or transceiver in a data recorder located outside the body. The capsule may also include a radio receiver for receiving instructions or other data from a base-station transmitter. Instead transmitting in a radio frequency, lower frequency electromagnetic signals may be used. Power may be supplied inductively from an external inductor to an internal inductor within the capsule or from a battery within the capsule.
An early example of a camera in a swallowable capsule is described in the U.S. Pat. No. 5,604,531, issued to the Ministry of Defense, State of Israel. A number of patents assigned to Given Imaging describe more details of such a system, using a transmitter to send the camera images to an external receiver. Examples are disclosed in U.S. Pat. Nos. 6,709,387 and 6,428,469. There are also a number of patents to the Olympus Corporation describing a similar technology. For example, U.S. Pat. No. 4,278,077 shows a capsule with a camera for the stomach, which includes film in the camera. U.S. Pat. No. 6,800,060 shows a capsule which stores image data in an atomic resolution storage (ARS) device.
An advantage of an autonomous encapsulated camera with an internal battery is that the measurements may be made with the patient ambulatory, out of the hospital, and with only moderate restrictions of activity. The base station includes an antenna array surrounding the bodily region of interest and this array can be temporarily affixed to the skin or incorporated into a wearable vest. A data recorder is attached to a belt and includes a battery power supply and a data storage medium for saving recorded images and other data for subsequent uploading onto a diagnostic computer system.
A typical procedure consists of an in-patient visit in the morning during which clinicians attach the base station apparatus to the patient and the patient swallows the capsule. The system records images beginning just prior to swallowing and records images of the GI tract until its battery completely discharges. Peristalsis propels the capsule through the GI tract. The rate of passage depends on the degree of motility. Usually, the small intestine is traversed in 4 to 8 hours. After a prescribed period, the patient returns the data recorder to the clinician who then uploads the data onto a computer for subsequent viewing and analysis. The capsule is passed in time through the rectum and need not be retrieved.
The capsule camera allows the GI tract from the esophagus down to the end of the small intestine to be imaged in its entirety, although it is not optimized to detect anomalies in the stomach. Color photographic images are captured so that anomalies need only have small visually recognizable characteristics, not topography, to be detected. The procedure is pain-free and requires no anesthesia. Risks associated with the capsule passing through the body are minimal; certainly, the risk of perforation is much reduced relative to traditional endoscopy. The cost of the procedure is less than that of traditional endoscopy because of the decreased requirements in clinician time, clinical facilities and anesthesia.
As the capsule camera becomes a viable technology for inspecting gastrointestinal tract, various methods for storing its image data have emerged. For example, U.S. Pat. No. 4,278,077 discloses a capsule camera that stores image data in chemical films. U.S. Pat. No. 5,604,531 discloses a capsule camera that transmits image data by wireless to an antenna array attached to the body or provided inside a vest worn by the patient. U.S. Pat. No. 6,800,060 discloses a capsule camera that stores image data in an expensive atomic resolution storage (ARS) device. The stored image data may then be downloaded to a workstation, which is normally a personal computer for analysis and processing. The results may then be reviewed by a physician using a friendly user interface. However, these methods all require a physical media conversion during the data transfer process. For example, image data on chemical film are required to be converted to a physical digital medium readable by the personal computer. The wireless transmission by electromagnetic signals requires extensive processing by an antenna and radio frequency electronic circuits to produce an image that can be stored on a computer. Further, both the read and write operations in an ARS device rely on charged particle beams.
A capsule camera using a semiconductor memory device, whether volatile or nonvolatile, is capable of a direct interface with a CMOS or CCD image sensor, where the image is captured, and a personal computer, where the image may be analyzed. The high density and low manufacturing cost achieved in recent years made the semiconductor memory the most promising technology for image storage in a capsule camera. According to Moore's law, which is still believed valid, the density of integrated circuits doubles every 24 months. Meanwhile, CMOS or CCD sensor resolution continues to improve, doubling every few years. Recent advancement in electronics also facilitate development in capsule camera technology. For example, (a) size and power reductions in light emitting diodes (LEDs) promotes the use of LEDs as a lighting source for a capsule camera; (b) new CMOS image sensors also reduce power and component count; (c) the continued miniaturization of integrated circuit allows integrating many functions on a single silicon substrate (i.e., system-on-a-chip or “SOC), resulting in size and power reductions.